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2017 Short/Medium Range Severe Thread


Hoosier

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SPC shifted the marginal area north some especially for IN/W OH.

Quote

   Day 2 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   1103 AM CST Fri Nov 17 2017

   Valid 181200Z - 191200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID
   MISSISSIPPI INTO THE OHIO VALLEY...

   ...SUMMARY...
   A few strong to severe storms capable of marginal hail or damaging
   wind gusts will be possible Saturday mainly over the Ohio Valley
   region.

   ...Synopsis...
   A strong shortwave trough will move from the Plains to the MS Valley
   during the day, with a deepening surface low moving from St. Louis
   to Lake Erie. A rapid increase of winds aloft will occur with a 100
   kt midlevel jet into the OH Valley by 00Z. A strong cold front will
   sweep eastward with southwesterly surface winds bringing a narrow
   plume of mid 50s to lower 60s dewpoints northward into IL and IN.
   Warm air advection in the low-levels will further be augmented by a
   50-60 kt low-level jet. Despite the favorable synoptic scale setup,
   instability will be minimal, with only a few marginally severe
   storms expected during the day.

   ...Mid MS into the OH Valleys...
   An area of mainly elevated thunderstorms is expected to occur early
   in the day, perhaps across eastern MO, and then developing eastward
   across IL and IN, with lift aided by warm air advection. Forecast
   soundings show sufficient instability for marginally severe hail.
   Other activity, perhaps surface based, will occur near the low, and
   southward along the cold front. The main detriment to a more
   substantial severe wind event appears to be the lack of heating,
   with weak low-level lapse rates. This should keep warm sector
   activity immediately along the front. Strong wind gusts will occur
   with the frontal passage, and some of this could be convectively
   enhanced.

   Farther south into TN, MS, and AL, instability will be even less,
   with a capping inversion preceding the front. Here too, some
   convectively augmented wind gusts will be possible during the
   afternoon and early evening.

   ..Jewell.. 11/17/2017

 

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I'm not extremely optimistic for surface based storms or a severe threat this far north, but can't help but get a bit excited about the potential for some training storms on the nose of the very strong LLJ.  With that said, models often seem to underdo the temps in the warm sector during the cold season when there's strong WAA, and some of the shorter range guidance suggests surface based instability and much less of an inversion as far north as I-70 or so in IN and OH, so it wouldn't surprise me if some areas see some damaging winds with any storms into central and southern IN and OH.  The HRRR also shows some modest rotating storms north of the warm front, so if the mid-level lapse rates aren't completely overturned the threat for some marginal hail could be there a little farther north...though I'm not extremely impressed looking at some of the forecast soundings north of the warm front.  

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Looks like Frankfort will be surveyed tomorrow.  From the limited number of pics I saw, some of the damage characteristics were more typical of what you'd see in a tornado (projectile 2x4 through a car window, debris wrapped around power lines, etc.) but that stuff is not really conclusive so we'll see how they characterize it.

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46 minutes ago, Chinook said:

Would you consider Nov. 18th to have been a tornado outbreak?

Personally, I think it's questionable, especially since it's easier to confirm the brief tornadoes nowadays.  I would call it a severe weather outbreak though, even though it's not the most impressive thing we've ever seen.

171118_rpts_filtered.gif.a8a87f756119cf9cce6cd1c46d0b49be.gif

 

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GFS continues to intrigue me around December 5th. 

990 low over Minnesota. Dew points mid 50s-60 from the gulf to Chicago. 

Sounding is not impressive at this time with a pretty substandard wind profile(vbv). It's obviously a long ways out...

 

If anything this might hold the potential for a high shear/low cape event. I've had my eye on this time frame for a few days now and figured it might be appropriate to post here. 

 

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IMG_0651.PNG

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Might be something to watch but it's so far out that it's kinda hard to speculate.  Ideally would like to see a longer period of moisture return prior to the system ejecting out but nonetheless we end up with decent dews by cool season standards (as currently progged, of course).

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You would think one of these days something would pop with all this abnormal warmth. I remember some people commenting in the days leading up to 11/17/13 that you don't get 70s that far north in mid-Nov without paying for it. Well here we are getting 60s even further north than that in late Nov and into Dec. So far everything is/looks to be moisture starved.

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Well, looks like a possibility for at least a lower end severe threat Monday into Tuesday for a chunk of the region. Instability is rather meager but wind fields are fairly impressive, so you know how that works in that even shallow rain/convection sometimes results in severe gusts.  The ECMWF solution with the quicker bombing low would probably result in a slightly better threat, relatively speaking, but the thermodynamics just aren't that good.

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22 minutes ago, CheeselandSkies said:

Interesting (and annoying) that the 12Z GFS portrays the best instability over MN into northern WI. Gets up to over 800 j/kg at 18Z near the Twin Cities. Where are systems like this in May/June?

>100 knots at 500mb, 50s dews well into WI in Dec., and the best we can do is a general thunder risk?

 

That area has better mid level lapse rates. Pretty good lapse rates actually.

I think they will probably pull the trigger on at least a marginal risk at some point.  It may be a long one too from the area you mentioned (MN/WI) southward.

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Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1140 PM CST Sat Dec 02 2017

   Valid 041200Z - 051200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM FAR EASTERN
   OKLAHOMA TO THE MID MISSISSIPPI VALLEY...

   ...SUMMARY...
   A few thunderstorms may produce strong, gusty winds from parts of
   the southern Plains to the mid Mississippi Valley Monday evening.

   ...Far eastern Oklahoma to the mid Mississippi Valley...
   A broad zone of cyclonic mid-level flow will expand eastward across
   the central US Monday, as a potent impulse lifts from the central
   Plains northeastward to the upper Great Lakes and another dives
   south across the Dakotas. The resultant surface pattern will feature
   a deepening cyclone lifting northeast across the upper Mississippi
   Valley with an attendant cold front sweeping east towards the Ohio
   and Tennessee Valleys overnight.

   Ahead of this front, modest low-level moisture (e.g., surface dew
   points in the upper 50s and lower 60s) will stream
   north/northeastward during the day. Surface heating will not be
   particularly impressive across the pre-frontal warm sector, but a
   narrow corridor of surface-based CAPE around 250-600 J/kg will
   likely materialize from eastern Oklahoma to parts of the mid
   Mississippi Valley. In turn, a thin/low-topped band of convection is
   expected to develop by the evening hours and accelerate eastward
   with the front. Despite the meager buoyancy, considerable
   low/mid-level flow upwards of 40-60 kt may support a few stronger
   gusts in the heartiest of convective elements, primarily during the
   evening hours. Additionally, the strength of low-level shear
   suggests a tornado cannot be ruled out. In turn, marginal
   probabilities have been introduced.

   ..Picca.. 12/03/2017

 

swody2_severeprob.png.bc2b26a36ce3021b7896f20ce7d89ace.png

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